In vehicles such as an automobile, a bus, and a truck, a wiper blade is used in order to ensure driver's view by wiping attachments such as rain, snow, insects, and muddy water splashed by a forward-running vehicle on a windshield such as a front windshield and a rear windshield.
A blade rubber provided in the wiper blade is normally formed such that natural rubber (NR) or a blend (NR/CR) of natural rubber and chloroprene rubber is cross-linked by sulfur. However, the NR has superior durability (low-temperature performance) at a low temperature, but has inferior durability (heat resistance) at a high temperature. The NR/CR has superior heat resistance, but has inferior low-temperature performance. Further, both of the NR and the CR are diene-based rubbers, and therefore, carbon-carbon bond is unstable. Accordingly, the NR and the CR easily react with ozone, oxygen, chemical reagents, and others, and thus the NR and the CR have inferior durability (weather resistance, ozone resistance, and chemical resistance) against weather, ozone, and chemical reagents.
On the other hand, ethylene-propylene-diene terpolimer rubber (EPDM) which is non-diene-based rubber (preferably polymer containing a small content of ethylene, and more particularly, polymer without adding oil or polymer blended with using oil having a low pour point) has superior weather resistance, ozone resistance, or others, and besides, has low-temperature performance equivalent to that of the NR and heat resistance superior to that of the NR/CR, and therefore, has superior durability. However, since the EPDM does not have a double bond in its main chain, there is a problem that its surface cannot be modified by an addition reaction with chlorine. Accordingly, its friction cannot be reduced as low as required for the wiper, and it is difficult to improve its wiping performance to be a practicable level.
Therefore, various techniques for using the EPDM in the blade rubber have been proposed. For example, Patent Documents 1 to 3 propose a multi-color extrusion molding (co-extrusion) in which the EPDM is used for a structure including a neck and the diene-based rubber is used for a lip portion for wiping a glass. Further, for example, Patent Documents 4 and 5 propose a treatment of performing a substitution reaction with halogen to EPDM.
On the other hand, as the method of modifying the rubber surface of the blade rubber, a method of modifying the surface with using an irradiation treatment has been proposed (for example, see Patent Document 6).